The present invention relates to the application of wideband radar signals. In particular, the present invention is directed toward a technique for using wideband radar signals to measure the interaction between a tire and the soil in vehicle mobility assessment.
Wheeled vehicle mobility depends in part on the interface between the tire and the on- or off-road surfaces on which the tire is operating. Studies of the interaction between a tire and soil, as a vehicle moves off-road, provides engineers information from which to draw conclusions about optimum tire design to maximize performance of the vehicle.
Traction of a wheeled vehicle is dependent largely upon the footprint of the tire. As soil deforms below the tire, the tire will passively shape itself to this deformation. Immobilization of the vehicle occurs when the sinkage of the tire and the net pull of all tires on the vehicle (referred to as xe2x80x9cdrawbar pullxe2x80x9d) reduce the traction of the vehicle to zero.
The interaction of vehicle tires and the soil is a subject of great concern. In military and emergency vehicle applications, vehicle immobilizion can have disastrous results. Moreover, an increasing number of civilian vehicles (e.g., SUVs, light trucks, and the like) are marketed with both off- and on-road capabilities. Thus, there is a pressing need to be able to study the interaction of vehicle tires and soil.
However, tire/soil interaction is difficult to study in real time since the presence of the tire itself prevents direct observations of any rutting or slippage under dynamic loading conditions. Large discontinuous deformations of soils are a key problem in vehicle mobility developments. Any attempt to place sensors in the soil may result in an intrusion into the soil resulting in variation in the soil parameters which the tire sees. Thus, what is required in the art is a method and apparatus which aids in the real-time study of soil/tire interaction.
In addition to testing purposes, a means of gathering tire/surface data in real time may be useful for other purposes as well. For example, such a system could be used with on-board vehicle traction control, dynamic braking (e.g., anti-lock controls), vehicle yaw controls, tire inflation and monitoring systems, and the like.
Such real-time data could be used to monitor relative traction at a given wheel and thus control power application to a given wheel before slippage occurs (as opposed to many present systems, which require wheel slippage before a given wheel is de-powered). Moreover, such real-time data could be useful in advising a driver of on- or off-road surface conditions (e.g., icing, snow, mud viscosity, and the like). Thus, for example, a driver could be alerted to the presence of black ice.
Prior art tire testing systems generally deal with looking for defects (occlusions and the like) within ties for production testing purposes, or are directed toward on-road testing techniques. Jones et al., U.S. Pat. No. 5,837,897, issued Nov. 17, 1998 and incorporated herein by reference, discloses an ultrasonic device for tire testing which may be used to determine tire pressure.
Matrascia, et al., U.S. Pat. No. 5,777,220, issued Jul. 7, 1998 and incorporated herein by reference, discloses a testing braking and traction of a wheel. Matrascia places the wheel/tire assembly onto a roller representing a road surface and tests the tire in that environment. Such testing techniques are known in the art, and while may provide adequate tire/road data, do not provide in situ tire/road data or off-road tire/soil data. Boyd, U.S. Pat. No. 3,948,080, issued Apr. 6, 1976, and incorporated herein by reference, discloses an apparatus for testing traction properties of pneumatic tires. Boyd provides a wheel with an instrumented hub which is then placed on a test trailer which is towed over a road surface. While this system may provide in situ data, it may have limited use in off-road data acquisition. Moreover, the apparatus does not provide real-time data on tire footprint or soil depression.
Recent advances in micro-impulse radar technology (MIR) have been developed at Lawrence Livermore Laboratories. Thomas E. McEwan has developed a number of applications for MIR technology. Representative of this technology is McEwan, U.S. Pat. No. 5,757,320, issued May 26, 1998 and incorporated herein by reference. MIR technology has been applied to a number of areas, including hidden object locators (i.e., xe2x80x9cstud finderxe2x80x9d), ground radar for finding buried objects (e.g., pipes, cables, and the like) as well as proximity sensors for car parking and cruise control systems. Some of these technologies are presently in production and may be commercially available.
However, to date, applicant is not aware of any activity, other than the inventor""s, in applying MIR or other types of radar technology to the field of tire testing, particularly for off-road tire testing to quantify tire/soil interaction.
The present invention comprises a radar system which may be mounted within the casing of a vehicle tire to measure the location of the inner casing of the tire (tire deformation) as well as the location of the tire/soil interface (tire footprint). The radar system of the present invention may also be used to determine soil characteristics by analyzing the reflected signals.
The present invention may have particular use in testing tires for use with on- or off-road surfaces. However, the present invention may also be used to monitor tire deformation, traction, footprint, and soil characteristics.
The present invention comprises a system for generating at least one of tire, ground, and tire/ground data for a pneumatic tire having a casing forming a hollow inner portion for containing a gas, the pneumatic tire being in contact with a ground surface. The system comprises a radar transmitter, located within the hollow inner portion of the pneumatic tire, for generating a radar signal towards a portion of the pneumatic tire in contact with the ground surface. A radar receiver receives a reflected signal from at least one of an interface between the gas and the casing and an interface between the casing and the ground surface. A means is provided for analyzing the reflected signal to produce at least one of tire, ground, and tire/ground data.
In the system of the present invention, the radar signal may comprise an ultra-wide band radar pulse. The radar transmitter comprises a pulse repetition rate function generator for generating a pulse signal for triggering a radar pulse, an impulse function generator, coupled to the pulse repetition rate function generator, for receiving the pulse signal and generating a wide-band radar impulse in response to the pulse signal, a first amplifier, coupled to the impulse function generator, for amplifying the radar impulse and outputting an amplified radar impulse, a waveguide, coupled to the amplifier, for receiving and transmitting the amplified radar impulse, and a feedhorn, coupled to the waveguide, for receiving the amplified radar impulse and transmitting the radar impulse toward the tire casing.
The radar comprises a switch, coupled to the pulse repetition rate generator and the radar feedhorn, for alternately receiving an input pulse from the pulse repetition rate generator and radar return signals from the radar feedhorn, a second amplifier, coupled to the switch, for amplifying the input pulse and the radar return signals, a detector, coupled to the second amplifier, for detecting radar return pulse data from the radar return signals, and a data port, coupled to the detector, for outputting radar return pulse data.
The apparatus of the present invention may map dynamic deflection of the tire. To this end, the invention provides insight into contours of the tire during interaction of the tire and any contact surface. Definition of contact surfaces as a result of theses internal tire contours provides information supporting objective quantification of traction performance of a tire. The device provides insight into claims of tire manufacturers regarding the ability of the tire to prevent hydroplaning of wet surface. Furthermore, the device, when used in conjunction with central tire inflation systems and active suspension systems, may provide required information such that the devices can react to limitations in traction. Moreover, given that ride performance and tire traction of a vehicle are directly related to pressure, contact pressure, and dynamic deflections of the tire, the device may be used to support research, testing, and development in this arena.